Synthetic polymers and shaped articles therefrom



Patented Aug. 27, 1940 UNITED STATES SYNTHETIC POLYMERS AND SHAPED ARTICLES THEREFROM George DeWitt Graves, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application February 15, 1937,

Serial No. 125,926 I Claims.

amides.

The materials used and improved by the practice of this invention are the new polymeric materials described in Patents 2,071,250, 2,071,253, and 2,130,948. In these cases there is described a new class of fiber-forming materials referred to as synthetic linear condensation polymers of which the polyamides described in the last two mentioned cases are the most useful. These fiber-forming polyamides are made by subjecting bifunctional polyamide-forming reactants, which may, for example, be a polymerizable amino acid alone or a mixture of diamine and dibasic acid, to polymerizing conditions until the polyamide formed is capable of being drawn 0 into filaments which possess the unusual property of being capable of being cold drawn, that is drawn or elongated under application of stress in the solid state, into fibers showing upon X-ray examination orientation along the fiber axis.

While the properties of the synthetic linear condensation polyamides will of course vary somewhat with the extent to which they have been polymerized and with the nature of the reactants used in their preparation, common characteristics of fibers derived from these polyamides are high tenacity, both wet and dry; high degree of orientation; extraordinary resistance to solvents and chemical reagents; exceptionally good elastic recovery; good dyeing properties; and good aging characteristics in air even at elevated temperatures. These polymers are generally crystalline and can be formed not only into filaments but also into other useful articles such as ribbons, foils, films, sheets, and the like. However, the sheeted products, e. g., films, sheets, etc., have the disadvantage of being opaque unless some special means such as described herein is used in their preparation. With regard to the oriented fibers as heretofore made the cold drawing of the polyamide filaments as previously practiced is satisfactory in the production of fibers of the smaller deniers, but as explained in more detail below filaments of the larger sizes cannot be satisfactorily cold drawn into oriented products.

The term filament as used herein refers to both the oriented and unoriented filaments or threads which are prepared from these polymers regardless of whether the filaments or threads are long (continuous) or short (staple), while the term fiber refers more specifically to the oriented filaments or threads.

In the manufacture of filaments and fibers a valuable property of these polyamides is that they can be spun into filaments directly from melt. Thus, fibers can be prepared from the polyamides by extruding the molten polymer through a suitable orifice into air and cold drawing the resultant filaments. For most purposes the fibers are more useful than the undrawn filaments from which they are derived, since they are tougher and more elastic. In preparing fibers of the size (usually 0.2 to 20 denier) used in the manufacture of fabrics, no difficulty is encountered in melt spinning tough filaments which cold draw readily. However, when it is endeavored to prepare large filaments or articles, such as bristles, ribbons, and rods, from the polyamides by this method, the products are inclined to be somewhat brittle, at least they are much less tough than the fine filaments mentioned above. As a result of this lower degree of toughness, these larger articles are much less susceptible to cold drawing for the production of products which for many purposes are more useful because of fiber orientation.

An object of this invention is to improve the utility of synthetic linear condensation polymers. Another object is to improve the properties, particularly the toughness, of fiber-forming synthetic linear condensation polyamides. A further object is to provide an improved method for preparing shaped articles from molten polyamides of this type. A further object is to improve the drawability of filaments made from said polyamides. A further object is the manufacture of new and useful shaped objects from synthetic linear condensation polymers. Other objects will appear hereinafter.

In its broader aspects this invention accomplishes these objects by rapidly chilling a hot fiber-forming synthetic linear condensation polymer. In its preferred embodiment this invention attains these objects by rapidly chilling a hot fiber-forming synthetic linear condensation polyamide in predetermined shape with a liquid which has no appreciable solvent action on the polyamide under the conditions of operation.

The rapid chilling of hot or molten fiberforming linear condensation polymers as referred to above results in a much tougher product than is obtained by slow cooling. This rapid cooling or tempering can be efie'cted by means of a cold liquid which does not dissolve or react with the polymer under the conditions of operation. The process of cooling hot or molten polyamides with the use of a liquid will be referred to herein as quenching. Quenching provides an excellent means of preparing articles of high toughness and improved utility directly from the molten polymer. The method is particularly well adapted to the preparation of large filaments, films, ribbons, rods, and the like. The improved toughness obtained by quenching such Although air cooling products greatly improves their drawability. Thus, filaments of 0.020 inch diameter spun from molten polymer having an intrinsic viscosity of 0.8 and cooled in air cannot generally be cold drawn at the ordinary speed of drawing, whereas quenched filaments of the same diameter and intrinsic vicosity can be readily drawn. is generally sufficient to produce the necessary tempering in the case of small diameter articles, such as filaments to be used in fabric manufacture, these articles can also be prepared to advantage by the quenching method herein described.

This invention therefore consists essentially in rapidly chilling a hot polyamide, preferably in predetermined shape, with a non-solvent liquid medium. The preferred procedure consists in extruding a molten polyamide in suitable form directly into the liquid medium. The polymer may be molten when it comes in contact with the liquid or it may be set or partially set due to the preliminary cooling action of air. To obtain the most pronounced effect, the temperature of the polyamide should not be materially below the melting point of the polyamide when it comes in contact with a liquid cooling medium. Thus, in the case of polyhexamethylene adipamide, which has a melting point (in absence of oxygen) of about 263 C., it is desirable that the temperature of the polyamide be above 245 C. when it comes in contact with the quenching medium. The melting point of the polyamides will of course vary depending upon the reactants from which they have been prepared. The most useful polyamides have melting points between 150 and 300 C. Although a large diiference in temperature between the molten polyamide and the cooling medium is desirable, it is generally inadvisable to heat the polyamide much above 300 C. since this tends to bring about thermal decomposition in most instances.

The liquid used to quench the polyamide should preferably be chemically inert toward the polyamide and should not have an appreciable solvent action thereon under the conditions of quenching. Water meets these requirements and in addition is readily available and has a high specific heat. It is therefore the preferred quenching medium. However, a large variety of other liquids may be employed. As examples might be mentioned alcohols, ketones, ethers, esters, hydrocarbons, chlorinated hydrocarbons, etc. The quenching liquid may consist of a mixture of compounds. It may: also contain wetting agents, dyes, etc. The quenching liquid is ordinarily employed at ordinary temperatures but may be cooled with the use of brine or other suitable means to sub-normal conditions, e. g., 0 0., in the case of water in order to obtain a larger temperature differential between the polyamide and the liquid. It is also within the scope of this invention to use the quenching medium at moderately elevated temperatures, e. g., 50-100 0., providing there is a sufiicient temperature differential. The temperature of the liquid should preferably be kept below C. If desired, the temperature of the liquid cooling medium may be regulated or kept constant by any suitable means. The liquid may be used in the form of a bath or spray.

As already indicated, polyamides which have been quenched are tougher than those which have not received this treatment. Thus, ribbons of 0.1 inch thickness extruded from molten polyamide and allowed to cool in air are rather brittle and cannot be given sharp bends without breaking. On the other hand, a similar ribbon prepared from the samemolten polymer by extrusion into water is quite tough and can readily be bent without breaking. This toughness improves the cold drawing properties of the polymer. In other words, the force required to cold draw ribbons and the like made by quenching is less than that required to draw similar articles prepared from the same polymer without quenching. For this reason it permits the cold drawing of articles of larger diameter than is otherwise possible. The improvement in drawing qualities results primarily from the quenching treatment and not from the action of the water itself, for an improvement in; drawing qualities is also obtained when a liquid such as carbon tetrachloride or pyridine is employed as the quenching medium. However, as indicated in Patent No. 2,137,235 treatment of the filaments with water until saturation is reached further improves their drawing properties. The following data illustrate the difference in drawing qualities of unquenched and quenched filaments of 0.028 inch diameter prepared from the same polyamide (intrinsic viscosity about 0.95). In each case the filaments were soaked in water before drawing. The force required to cold draw the unquenched (i. e., spun under non-tempering conditions) was 3.0 pounds, whereas the force required to cold draw the quenched filament was only 1.4 pounds. Not only are the drawing qualities of the quenched filament better, but the strength of the cold drawn product is higher. The average tenacity of oriented bristles made from quenched filaments of polyhexamethylene adipamide having an intrinsic viscosity of approximately 0.9 is 4.7 g. per denier at the breaking point, whereas the average strength of oriented bristles prepared from the same polymer under non-quenching conditions is 3.0 g. per denier at break.

Quenching is also of importance in connection with the preparation of polyamides in sheet form. If films or sheets are prepared by allowing a layer of molten polyamide to cool slowly, e. g., on a glass plate in air, the product is opaque. On the other hand, if the molten layer of polyamide is rapidly chilled by quenching with water or Other suitable liquid, it is much less opaque and is usually clear and transparent. Microscopic examination indicates that this transparency of the tempered films is due to the fact that they are made up of minute crystal aggregates (less than 20 microns and usually less than 2 microns in diameter), whereas the crystal aggregates in opaque polyamide films, e. g., those prepared without tempering, are much larger.

Reference has been made to the degree of polymerization and to the intrinsic viscosity of polyamides. Intrinsic viscosity, which furnishes a rough comparison of the molecular weight of different polyamides, is defined as 1 2. 11. C where m is the viscosity of a dilute meta-cresol solution of the polyamide divided by the viscosity of meta-cresol in the same units and at the same temperature and C is the concentration in grams of polyamide per 100 cc. of solution. In general, polyamides do not exhibit fiber-forming qualities unless their intrinsic viscosity is greater than 0.4. The strength and toughness of polyamides improve with increase in intrinsic viscosity. For the preparation of most shaped articles it is desirable to use polyamides having an intrinsic viscosity above 0.6, polyamides having intrinsic viscosities between 0.8 and 2.0 being particularly useful. Quenching frequently permits the preparation of shaped articles from polyamides of lower intrinsic viscosity than would otherwise be possible. For example, in the preparation of bristles, it is possible by application of quenching to prepare satisfactory bristles using polyamides having intrinsic viscosities as low as 0.65, whereas polyamides having an intrinsic viscosity above 0.90 are usually required to prepare satisfactory bristles if quenching is not employed.

Although I do not wish to be bound by my explanation of the quenching phenomenon, I believe that the polyamides exist in at least two diiferent crystalline forms and that quenching leads to the production of a crystalline form which is difierent from that obtained by slow cooling. X-ray diffraction data offer support of this theory. The X-ray patterns of both quenched and unquenched massive polyamides are characterized chiefly by two heavy rings which arise from diffraction of the X-rays by the principal spacings of the polymers, and by fogging which arises from other spacings either normal or strained. In the pattern of quenched polyhexamethylene adipamide, for example, the two prominent rings represent spacings of about 4.32 A. and 3.82 5., while in unquenched polyhexamethylene adipamide one is 4.32 A. but the other is 3.68 A. When specimens of the two materials are cold drawn, the difiraction patterns show orientation; breaking of the rings into arcs occurs to the same degree in each and the spacing diiference observed in the massive form remains.

The following examples describe the invention in greater detail:

Example I A sample of polyhexamethylene adipamide (derived from hexamethylenediamine and adipic acid) having an intrinsic viscosity of approximately 0.80 was formed into bristles as' follows. The molten polymer was spun directly from the autoclave in which it was prepared by extrusion through a spinneret aperture 0.055 inch in diameter attached to the bottom of the autoclave. The spinning was effected at 290 C. under a pressure of 200 lb./sq. in., applied with oxygenfree nitrogen. The filament was extruded at a rate of 120 ft./min. into a bath of cold water placed 2.5 inches below the spinneret orifice. The filament obtained in this way had a diameter of approximately 0.023 inch. The filament was quite tough and could be cold drawn without breakage. However, it was found that soaking the filament in water for eighteen hours prior to drawing facilitated the cold drawing operation. Filaments which were cold drawn 300%, i. e., until the length was four times that of the original filament proved very useful as artificial bristles.

When filaments of the same size were melt spun from the above polyamide without quenching, the product was less tough than that described above and could not be cold drawn satisfactorily due to breakage.

Example H solution of the polymer in formic acid on a glass plate and allowing the solvent to evaporate. The film obtained in this way was opaque. The glass plate and film were then heated above the melting point of the polymer until the latter melted and became clear and transparent. The plate and film were then plunged into cold water. The polyamide solidified yielding a transparent film of good clarity which could be oriented by application of stress.

Example III Polyhexamethylene adipamide of intrinsic viscosity 0.90 was prepared by heating with stirring 786 parts by weight of hexamethylene diammonium adipate and a viscosity stabilizer consisting of 5.7 parts by weight of adipic acid and 4.6 parts by weight of hexamethylene diammonium acetate in an oxygen-free atmosphere for 1.5 hours at 290 C. The autoclave was then evacuated to 60 mm. for five minutes, oxygen-free nitrogen was introduced, and the melt held at 290 C. for one hour. The molten polyamide was then extruded from the bottom of the autoclave through a tube having an inside diameter of 0.25 inch, the lower end of which was situated 0.25 inch above the bite of two forming rolls which were immersed to one-half their diameter in cold water and were operated by a variable speed motor. The extruded polymer passed between the rolls and was quenched, as soon as it was shaped, by the water in which the rolls were immersed. The extruded polymer was thus formed into ribbons, 0.5 inch wide and one of the rolls.) The ribbon was very tough, strong, and pliable. It could be bent double without breaking and could be cold drawn into an oriented ribbon. On the other hand, ribbons prepared in the same way but without quenching were much less pliable.

Although this invention has been described with particular reference to polyamides, it is applicable broadly to fiber-forming synthetic linear condensation polymers. As examples of such polymers might be mentioned polyesters, polyacetals, polyethers, polyester-polyamides, and ether copolymers. I

It is to be understood that the aforementioned examples are illustrative merely of the manner of carrying out the practical application of this invention. The process has been described with particular reference to polyamides because they form an especially useful class of polymers. A valuable class of polyamides for use in this invention comprise those derived from diamines of formula NH2CH2RCH2NH2 and dicarboxylic acids of formula HOOCCH2R'CH2COOH and amideforming derivatives of these reactants, R and R in said formulae representing divalent hydrocarbon radicals free from olefinic and aeetylenic unsaturation and R having a chain length of at least two carbon atoms. An especially valuable group of polyamides within this class are those in which R is (CH2): and R is (CH2)y wherein :1: is at least two. As examples of polyamides which fall within one or both of these groups might be mentioned polytetramethylene adipamide, polytetramethylene suberamide, polytetramethylene sebacamide, polypentamethylene sebacamide, polyhexamethylene adipamide. 1 polyhexamethylene beta-methyl adipamide. polyhexamethylene sebacamide, polyoctamethylene adipamide, polydecamethylene adipamide, polydecamethylene p-phenylene diacetamide, and poly-p-xylylene sebacamide.

This invention is also of importance in connection with linear condensation polyamides derived from monoaminomonocarboxylic acids and their amide-forming derivatives. As examples of such polyamides might be mentioned those derived from fi-aminocaproic acid, 9-aminononanoic acid, and ll-aminoundecanoic acid. It is also within the scope of this invention to quench mixtures of polyamides or interpolymers or copolymers, i. e., polyamides prepared from a mixture of polyamide-forming reactants, e. g., a

mixture of two or more diamines with one or more dicarboxylic acids, or a mixture of a diamine, a dicarboxylic acid, and an amino acid.

This invention is not limited to the quenching of polyamides and polyamide-articles consisting solely of fiber-forming linear condensation polyamides. Other materials such as plasticizers, melting point depressors, e. g., o-hydroxydiphenyl and diphenylolpropane, pigments, extenders, fillers, dyes, resins, oils, cellulose derivatives, and the like may be present in addition to the polyamide. Thus, a quenched polyamide filament containing 3% of titanium dioxide as a delusterant is tougher and more pliable than an unquenched filament of the same composition. The foreign material if present in moderate amounts does not interfere with the beneficial effects of the quenching operation.

It will be evident to those skilled in the art that the quenching can be effected in a variety of ways. It is not absolutely essential that the polyamide come in contact with the liquid medium, although this is the preferred procedure particularly when operating with articles, such as filaments, films, ribbons, and the like. It is within the scope of this invention, however, to impart toughness to polyamides by rapidly cooling the container containing the hot polyamide. Thus, it has been found that if the polyamide is heated in a suitable vessel and the vessel rapidly cooled with water, brine, or the like, the polymer obtained is tougher than that obtained by allowing the polymer to cool more slowly. For certain applications it is desirable in preparing polyamides to chill the polymer rapidly in r the reaction vessel in which it is formed, but in general it is more desirable to discharge the molten polymer directly from the reaction vessel into a suitable cooling liquid. This is particularly desirable when the polyamide is to be 55 used as such in the manufacture of shaped articles.

It will be evident from the foregoing discussion that this invention provides a simple and economical method for improving the properties of synthetic fiber-forming linear condensation polyamides. Application of this invention yields a tough, strong, and pliable polymer which has many applications in the art. The invention is particularly useful in the preparation of large polyamide filaments, bristles, films, sheets, ribbons, foils, and the like, since it greatly improves the drawing qualities of these articles. Another advantage in connection with films and sheets is that the process herein described improves the clarity of the products. Large filaments prepared by the process of this invention are useful as bristles, horsehair substitutes, mohair substitutes, tennis strings, musical instrument strings, surgical sutures, fish line leaders, dental fioss, and the like.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specific embodiments thereof except as defined in the appended claims.

I claim:

1.' A fiber-forming synthetic linear polyamide in the form of sheet material having crystal aggregates whose average diameter is two microns.

2. In the treatment of fiber-forming synthetic linear condensation polymers, the step comprising rapidly chilling the hot polymer with a liquid having substantially no solvent action on the polymer under the conditions used.

3. In the manufacture of shaped products from synthetic linear condensation polymers, the step comprising rapidly chilling the hot polymer in predetermined shape by quenching it in a liquid which has no substantial solvent action on the polymer under the conditions used.

4. In the manufacture of filaments from fiberforming synthetic linear condensation polymers, the steps comprising extruding filaments from the molten polymer, into a liquid which rapidly chills the filaments, said liquid having substantially no solvent action on the polymer, and cold drawing the filaments.

5. In the treatment of fiber-forming synthetic linear polyamides, the step comprising rapidly chilling the hot polyamide with a liquid when the polyamide is at a temperature not substantially below its melting point, said liquid having substantially no solvent action on the polymer under the conditions used.

6. In the manufacture of shaped products from synthetic linear condensation polyamides, the step comprising rapidly chilling the hot polyamide in predetermined shape by quenching it in a liquid which has no substantial solvent action on the polyamide under the conditions used.

'7. In the manufacture of shaped products from synthetic linear condensation polyamides, the step comprising rapidly ch'lling the hot polyamide in predetermined shape by quenching it in water.

8. In the manufacture of filaments from fiberforming synthetic linear polyamides, the steps comprising forming the molten polyamide into a filament and rapidly chilling the hot filament by quenching it in a liquid which has no substantial solvent action on the polyamide under the conditions of operation.

9. In the manufacture of large filaments including bristles, rods, and the like, the steps comprising forming a molten synthetic linear condensation polyamide into a filament, rapidly chilling the hot filament with a liquid having substantially no solvent action thereon, and cold drawing the filament.

10. In the manufacture of sheet material including films and ribbons, the steps comprising forming the sheet material from a molten fiberforming linear polyamide, and then rapidly chilling the hot polyamide by quenching it in a liquid having no substantial solvent action on the polyamide.

11. In the manufacture of shaped products from synthetic polyamides capable of being cold drawn into oriented fibers, the steps comprising shaping the desired product from the polyamide, and rapidly chilling said product when it is at a temperature below its decomposition point but less than.

not substantially below its melting point by in a liquid having no substantial solvent action means of a liquid having no appreciable solvent on the polymer.

action on the polyamide. 16. A fiber-forming synthetic linear poly- 12. The manufacture set forth in claim 6 in amide in the form of a shaped article having which said polyamide is obtained by reacting a crystal aggregates whose average diameter is less 5 diamine and a substance of the class consisting than two microns.

of dicarboxylic acids and amide-forming deriva- 17. A filament comprising synthetic linear poltives of dibasic carboxyllc acids. yamide having crystal aggregates whose average 13. The manufacture set forth in claim 6 in diameter is less than two microns.

which the polyamide is polymeric hexamethylene 18. Dental floss comprising synthetic linear 10 adipamide. polyamide having crystal aggregates whose aver- 14. The manufacture set forth in claim 10 in age diameter is less than two microns.

which the polyamide is polymeric hexamethylene 19. The manufacture set forth in claim 6 in adipamide. which said polyamide is polyhexamethylene se- 15. In the manufacture of sheet material inbacamide. 15

eluding films and ribbons, the steps comprising 20. The manufacture set forth in claim 8 in forming sheet material from a molten fiberwhich said polyamide is polyhexamethylene seforming linear condensation polymer, and then bacamide.

rapidly chilling the hot polymer by quenching it GEORGE DEWI'IT GRAVES. 

